Polyolefin moldings are often used as parts of automobile outer panels and domestic electrical goods for example, and more recently recycled polyolefin moldings have come to be reused. A primer which contains a chlorinated polyolefin is used in those cases where a two-liquid type top-coat paint which includes a polyisocyanate compound is used as the top-coat paint of a polyolefin molding in order to improve the adhesion of the top-coat paint film with the polyolefin molding. However, there is a problem in that the adhesion with the polyolefin base material is inadequate in cases where rubber products (such as styrene/butadiene rubber, isoprene rubber and the like) which have been included in polyolefin moldings and recycled polyolefin moldings to which only a small amount or no hydroxyl group containing polyolefin has been added are reused.
Furthermore, in those cases where repair-coating is carried out after a primer and a top-coat paint have been coated on a polyolefin molding, the paint film has generally been sanded to remove dirt and marks and then this part has been repainted (recoated) with primer and top-coat paint. At this time the recoating with primer and top-coat paint can be carried out on a paint film which has not been ground (unsanded) without grinding the whole surface of the paint film which is to be repaired. In such a case there is a problem in that the inter-layer adhesion of the under-layer paint film and the recoated primer is inadequate.
Paint compositions which have as essential components (A) chlorinated polyolefin resin which has a chlorine content of from 10 to 50 mass %, (B) acrylic modified chlorinated polyolefin resin, (C) acrylic resin and/or polyester resin of weight average molecular weight from 2,000 to 50,000 and hydroxyl group value from 10 to 90 mgKOH/g and (D) isocyanate compound in which the ratio of the isocyanate equivalent and the hydroxyl group equivalent [Isocyanate Equ.]/[Hydroxyl Group Equ.] is from 0.5/1.0 to 1.2/1.0 and in which, of the total mass (solid fraction) of the (A), (B) and (C) components, the (A) component accounts for from 3 to 20 mass %, the (B) component accounts for from 5 to 40 mass % and the (C) component accounts for from 40 to 92 mass % are known as two-liquid type paint compositions which have an excellent high gloss appearance, weather resistance, solvent resistance and coating operability as well as providing excellent adhesion on being coated directly without the application of a primer on polyolefin moldings with which adhesion is difficult to achieve (for example, see Japanese Unexamined Patent Application Laid Open 2005-139336). However, since these combine the function of a primer and the function of a top-coat paint the adhesion with polyolefin base material moldings is inadequate and, furthermore, there is a problem with the pot-life of these two-liquid type paints.
Furthermore, resin compositions for coating purposes which have good adhesion on polyolefin base materials which are characterized in that they include as essential components (1) polymer which has acetoacetoxy groups in a side chain which has been obtained by polymerizing or copolymerizing an acetoacetoxy group containing monomer with other copolymerizable monomer, as required, in the presence of from 5 to 50 parts by weight of a chlorinated polyolefin resin of chlorine content from 15 to 50 wt % and (2) isocyanate compound are known as resin compositions for coating purposes with which paint films which have excellent adhesion, hot water resistance and gasoline resistance can be formed and which also have excellent paint storage stability and which can be coated directly without the need for any pre-treatment such as coating with primer etc. on polyolefin base material moldings (for example, see Japanese Unexamined Patent Application Laid Open H8-311397). However, these resin compositions for coating purposes are two-liquid type paints and there are problems with the pot-life.
Furthermore, a primer for use on plastic which is characterized in that it contains (A) chlorinated polyolefin which has a chlorine content of from 16 to 22 wt % and of which the weight molecular weight is from 30,000 to 120,000, (B) blocked polyisocyanate where an isocyanurate type aliphatic and/or alicyclic polyisocyanate has been blocked with malonic acid di-alkyl ester and acetoacetic acid ester and (C) polyol resin is known as a primer for use on plastics which has excellent adhesion on polyolefin base material moldings and excellent recoat adhesion on paint films (for example, see Japanese Unexamined Patent Application Laid Open 2002-121462). However, although the adhesion is good with the polyolefin based base material molding and paint films which have been sanded, there is a problem in that the recoat adhesion is inadequate in the absence of sanding.
[Patent Citation 1]
    Japanese Unexamined Patent Application Laid Open 2005-139336[Patent Citation 2]    Japanese Unexamined Patent Application Laid Open H8-311397[Patent Citation 3]    Japanese Unexamined Patent Application Laid Open 2002-121462
The present invention is intended to provide primers which have excellent adhesion on plastic base materials, and especially on polyolefin base materials, and which have excellent inter-layer adhesion with underlying paint films, and especially urethane resin-based top-coat paint films, on recoating (repainting), and to provide a method of coating in which these primers are used.